One of the problems frequently encountered during the course of producing petroleum and other fluids from subterranean formations is the inadvertent flow of sand or other mineral particles from the petroleum formation along with the fluid being recovered into the producing wellbore. This is a well recognized problem and many undesired consequences result from this phenomena. The flow of sand into the wellbore can produce a cavity or zone of greatly weakened formation around the perforations of the wellbore, such that in severe cases, the formation will collapse and destroy the casing and cause loss of the well. Also, continued production of fluid with simultaneous flow of sand or other particulate formation matter from the formation into the wellbore will cause the wellbore itself to become plugged, which will prevent the further production of oil from that well. Finally, sand being transported to the surface of the earth along with fluids causes abrasive wear of the tubular goods and pumps utilized in production wells, which cause early failure of these expensive components.
The above problems have long been recognized and many procedures have been disclosed and employed with varying degrees of success for the purpose of controlling the production of sand along with formation fluids. Numerous techniques have been utilized, most having the common feature of employing methods and procedures with the hope of forming the stable permeable zone around the production means in the producing well such that fluid can be freely produced from the formation, while particulate matter such as sand or other formation particles are restrained from flowing to and through the perforations in the wellbore.
When the problem of sand flow has progressed over a long period of time without corrective measures being taken, substantial zones which have been washed out in the portion of the formation immediately adjacent to the wellbore are sometimes formed, and it is common practice in the oil field to apply techniques referred to generally as gravel packing in order to form a zone where the cavities previously existed which will facilitate production of fluids from the formation while restraining the movement of particulate matter such as sand into the wellbore. The term gravel is commonly used in this application somewhat loosely and refers generally to rigid particulate matter ranging in size from that of coarse sand to pebble size materials. Ordinarily, mineral materials constitute the gravel employed in these processes, although glass or ceramic particles may also be employed.
In most prior art methods, sand or gravel is placed in the washed out zones, after which some material is introduced into the gravel packed area to cement or bind the granular particles together so as to prevent the flow of these particles into the well once production is resumed.
One technique that has been utilized with varying degrees of success involves the injection of polymerizable resin into the gravel packed zone, or by the formulation of a slurry of the gravel precoated with resinous material which can be pumped into the washed out zone. After placement, the thermal setting resin bonds the particulate matter together to form a permeable, consolidated structure. This technique has been shown to be technically feasible, but it is expensive and not always entirely satisfactory. The weakness of prior art methods has been especially serious when attempt has been made to treat production wells formed in earth formations to which steam stimulation is being applied for the purpose of increasing the production of viscous petroleum. The high temperature fluids produced in such wells causes rapid deterioration of the resins utilized to bond the gravel particles together.
In U.S. Pat. No. 4,427,069, a method for consolidating sand naturally existing in an earth formation adjacent to a producing well utilizing as a polymerizable resin, a furfuryl alcohol oligomer, which produced a strong and durable resin bonding the sand grains together while still maintaining sufficient permeability to permit the production of fluid from the formation. This resin is particularly attractive in that it is stable at the high temperatures normally encountered during the passage of fluids from a formation which is being stimulated by steam flooding. In U.S. Pat. No. 4,428,427 which issued Jan. 31, 1984, a gravel pack forming technique employing a similar resin to precoat gravel or other particulate matter and introduce a fluid comprising the suspended granular material into the washed-out zone or cavity adjacent to producing well was disclosed.
Both of the above techniques have been very successful and shown to be more durable in high temperature operations than most other known sand consolidation or consolidated gravel pack methods; however, some problems have been encountered in connection with each method. In the sand consolidation method of U.S. Pat. No. 4,427,069, introduction of a resinous material into a sand zone in the formation does not accomplish completely uniform coating of the sand grains with resin as is possible if the particulate matter is coated with resin prior to introduction into the formation. The more successful technique involves the forming of a resin-coated gravel as described in U.S. Pat. No. 4,428,427 and introducing a suspension of this resin-coated gravel into the formation, after which the well is shut-in for a sufficient period of time to cause polymerization of the resin coating as a consequence of natural formation temperatures. While quite successful, the method is expensive, and a major portion of the expense is associated with the fact that the gravel is coated with resin, dried and stored in containers which can be easily transported from the plant where the resin-coating is applied to the particulate matter to the oil field. These containers of resin-coated gravel have been stored near the well where they are to be used until the appropriate time for formulating the consolidated gravel pack arrives. Since the resin constitutes the major chemical cost of the coated sand, but the gravel represents by far the larger portion of the total weight of the precoated gravel, the shipping cost for the resin coated gravel are quite high. Coating and drying costs are also quite high. Also, storage of the material during warm weather frequently causes undesired thermal polymerization of the resin-coated sand particles in the shipping container, rendering the material useless for the intended purpose.
Attempts to coat the gravel at the site where the consolidation procedure will be applied have not been altogether satisfactory because the resin-coated gravel has a tacky or sticky quality. It is difficult and expensive to dry these particles at the well site. Unless the particles are dried, however, suspension of the undried resin-coated gravel particles in an aqueous fluid for the purpose of the transportation down the wellbore and placement in the washed-out zone where the consolidated mass is desired, has resulted in the particles sticking together, which prevents forming a strong, uniform permeability consolidated gravel pack. Moreover, if the resin-coated particles are suspended in water, the water washes at least a portion of the resin off the sand or gravel grains, which reduces the ultimate strength of the consolidated gravel pack. If the particles are suspended in an oil based fluid, the resin absorbs oil from the carrier fluid which results in the resin becoming even more sticky and tacky than it was prior to contact with the oil.
In view of the foregoing discussion, it can be appreciated that there is a substantial unfulfilled commercial need for a technique for forming a consolidated gravel pack in a producing oil well to restrain flow of unconsolidated sand particles into the well, by a method in which the gravel particles are coated with resin at about the time and place that they are to be employed in the sand consolidation technique, without attempting to dry the particles, while avoiding the problem of washing resin off the resin-coated gravel particles or increasing the tackiness of these particles during the period when they are pumped down the tubing for placement in the zone of the formation adjacent to the producing well. For such a procedure to be successful, there is also a need to incorporate a catalyst in the resin-coated sand containing fluid whose activity is delayed until the resin-coated gravel has been placed in the washed out cavity adjacent to the producing well.
The present invention is directed to compositions and methods employing compositions whereby the above mentioned objectives and unfulfilled needs may be satisfied. The invention is directed toward methods of forming a composition comprising granular particles of mineral matter such as gravel coated with a heat polymerizable resin dispersed in a fluid which prohibits either removal of the resin coating from the sand grains or premature sticking of the resin-coated gravel grains together during the period while they are being formulated and pumped into the wellbore for the purpose of forming the consolidated gravel mass in the formation adjacent to the production means of the producing well.